Problem: 6 glue sticks cost $6.60. Which equation would help determine the cost of 3 glue sticks?
Solution: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 3 glue sticks. Since 3 glue sticks cost $x$ , we have the following proportion: $\dfrac{3}{x}$ We can write the fact that 6 glue sticks cost $6.60 as a proportion: $\dfrac{6}{\$6.60}$ The cost changes along with the number of glue sticks purchased, and so the two proportions are equivalent. $\dfrac{3}{x} = \dfrac{6}{\$6.60}$